README: need add meta-ruby to build qt5 image
README: need add meta-ruby to build qt5 image

Also fix a typo error.

Signed-off-by: Josh Wu <5d315a13f7549d1ecf8e62305448b567ef831df9@atmel.com>
Tested-by: Bo Shen <b3e6a3251704a94eee1cf08e0adc382e6cb535ee@atmel.com>

koenkooi/meta-atmel,alexandrebelloni/meta-atmel,kraj/meta-atmel,koenkooi/meta-atmel,alexandrebelloni/meta-atmel,kraj/meta-atmel,linux4sam/meta-atmel,kraj/meta-atmel,linux4sam/meta-atmel,alexandrebelloni/meta-atmel,linux4sam/meta-atmel,koenkooi/meta-atmel,linux4sam/meta-atmel,linux4sam/meta-atmel